As technology progresses, wireless devices tend to integrate more features and become increasingly ubiquitous. For example, wireless devices may include features associated with personal digital assistants (PDAs), cellular telephones, wireless internet access devices, global positioning system (GPS) receivers, and the like. Therefore, multiple radio frequency (RF) signals spanning a wide frequency range are common in many areas and may interfere with one another. Wireless devices may support one or more wireless communications protocols, such as third (3G), fourth (4G), or later generation cellular telephone protocols, GPS protocols, wireless fidelity (Wi-Fi) protocols, Bluetooth®, and the like. Some of these protocols may have tight channel spacings that require narrow channel bandwidths. Therefore, wireless devices using specified channel bandwidths may need RF filters that have required passbands to accept desirable signals and have maximum broadband rejection to remove interfering signals.
Surface acoustic wave (SAW) devices are electro-mechanical devices that utilize surface acoustic waves, which travel along the surface of a substrate having some elasticity. The substrate has a relationship between an electrical signal and mechanical movement within the substrate. An applied electrical signal may be used to cause the mechanical movement, which may include surface acoustic waves, or the mechanical movement may be used to provide an electrical signal. Therefore, the substrate may be used as a transducer for transduction between an electrical signal and mechanical movement. An inter-digital transducer (IDT) is a special type of transducer used to convert an electrical signal into surface acoustic waves or to convert surface acoustic waves into an electrical signal.
A SAW track may include two or more IDTs along an acoustic cavity, such that the IDTs are acoustically coupled to one another. A first IDT in the SAW track may receive an input signal and a second IDT in the SAW track may provide an output signal based on surface acoustic waves that are coupled between the IDTs. Multiple SAW tracks may be electrically coupled to one another to form a SAW device, such as a SAW filter. A SAW filter may be used in some RF applications to provide a required passband and good broadband rejection. Manufacturing costs of a SAW device may be directly related to the size of the SAW device, which is related to the sizes and spacings of IDTs used in the SAW device. Such sizes and spacings may be related to frequencies of surface acoustic waves in the SAW device. To preserve signal integrity in RF applications, a SAW device may need to have minimal insertion loss. Thus, there is a need for a SAW device having a small size, minimal insertion loss, a required passband, and maximum broadband rejection.